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[mediawiki.git] / includes / db / DatabaseIbm_db2.php

<?php
/**
 * This script is the IBM DB2 database abstraction layer
 *
 * See maintenance/ibm_db2/README for development notes and other specific information
 * @ingroup Database
 * @file
 * @author leo.petr+mediawiki@gmail.com
 */

/**
 * Utility class for generating blank objects
 * Intended as an equivalent to {} in Javascript
 * @ingroup Database
 */
class BlankObject {
}

/**
 * This represents a column in a DB2 database
 * @ingroup Database
 */
class IBM_DB2Field {
        private $name, $tablename, $type, $nullable, $max_length;

        /**
         * Builder method for the class 
         * @param Object $db Database interface
         * @param string $table table name
         * @param string $field column name
         * @return IBM_DB2Field
         */
        static function fromText($db, $table, $field) {
                global $wgDBmwschema;

                $q = <<<END
SELECT
lcase(coltype) AS typname,
nulls AS attnotnull, length AS attlen
FROM sysibm.syscolumns
WHERE tbcreator=%s AND tbname=%s AND name=%s;
END;
                $res = $db->query(sprintf($q,
                                $db->addQuotes($wgDBmwschema),
                                $db->addQuotes($table),
                                $db->addQuotes($field)));
                $row = $db->fetchObject($res);
                if (!$row)
                        return null;
                $n = new IBM_DB2Field;
                $n->type = $row->typname;
                $n->nullable = ($row->attnotnull == 'N');
                $n->name = $field;
                $n->tablename = $table;
                $n->max_length = $row->attlen;
                return $n;
        }
        /**
         * Get column name
         * @return string column name
         */
        function name() { return $this->name; }
        /**
         * Get table name
         * @return string table name
         */
        function tableName() { return $this->tablename; }
        /**
         * Get column type
         * @return string column type
         */
        function type() { return $this->type; }
        /**
         * Can column be null?
         * @return bool true or false
         */
        function nullable() { return $this->nullable; }
        /**
         * How much can you fit in the column per row?
         * @return int length
         */
        function maxLength() { return $this->max_length; }
}

/**
 * Wrapper around binary large objects
 * @ingroup Database
 */
class IBM_DB2Blob {
        private $mData;

        function __construct($data) {
                $this->mData = $data;
        }

        function getData() {
                return $this->mData;
        }
}

/**
 * Primary database interface
 * @ingroup Database
 */
class DatabaseIbm_db2 extends Database {
        /*
         * Inherited members
        protected $mLastQuery = '';
        protected $mPHPError = false;

        protected $mServer, $mUser, $mPassword, $mConn = null, $mDBname;
        protected $mOut, $mOpened = false;

        protected $mFailFunction;
        protected $mTablePrefix;
        protected $mFlags;
        protected $mTrxLevel = 0;
        protected $mErrorCount = 0;
        protected $mLBInfo = array();
        protected $mFakeSlaveLag = null, $mFakeMaster = false;
         *
         */
        
        /// Server port for uncataloged connections
        protected $mPort = NULL;
        /// Whether connection is cataloged
        protected $mCataloged = NULL;
        /// Schema for tables, stored procedures, triggers
        protected $mSchema = NULL;
        /// Whether the schema has been applied in this session
        protected $mSchemaSet = false;
        /// Result of last query
        protected $mLastResult = NULL;
        /// Number of rows affected by last INSERT/UPDATE/DELETE
        protected $mAffectedRows = NULL;
        /// Number of rows returned by last SELECT
        protected $mNumRows = NULL;
        
        
        const CATALOGED = "cataloged";
        const UNCATALOGED = "uncataloged";
        const USE_GLOBAL = "get from global";
        
        /// Last sequence value used for a primary key
        protected $mInsertId = NULL;
        
        /*
         * These can be safely inherited
         * 
         * Getter/Setter: (18)
         * failFunction
         * setOutputPage
         * bufferResults
         * ignoreErrors
         * trxLevel
         * errorCount
         * getLBInfo
         * setLBInfo
         * lastQuery
         * isOpen
         * setFlag
         * clearFlag
         * getFlag
         * getProperty
         * getDBname
         * getServer
         * tableNameCallback
         * tablePrefix
         * 
         * Administrative: (8)
         * debug
         * installErrorHandler
         * restoreErrorHandler
         * connectionErrorHandler
         * reportConnectionError
         * sourceFile
         * sourceStream
         * replaceVars
         * 
         * Database: (5)
         * query
         * set
         * selectField
         * generalizeSQL
         * update
         * strreplace
         * deadlockLoop
         * 
         * Prepared Statement: 6
         * prepare
         * freePrepared
         * execute
         * safeQuery
         * fillPrepared
         * fillPreparedArg
         * 
         * Slave/Master: (4) 
         * masterPosWait
         * getSlavePos
         * getMasterPos
         * getLag
         * 
         * Generation: (9)
         * tableNames
         * tableNamesN
         * tableNamesWithUseIndexOrJOIN
         * escapeLike
         * delete
         * insertSelect
         * timestampOrNull
         * resultObject
         * aggregateValue
         * selectSQLText
         * selectRow
         * makeUpdateOptions
         * 
         * Reflection: (1)
         * indexExists
         */
        
        /*
         * These need to be implemented TODO
         * 
         * Administrative: 7 / 7
         * constructor [Done]
         * open [Done]
         * openCataloged [Done]
         * close [Done]
         * newFromParams [Done]
         * openUncataloged [Done]
         * setup_database [Done]
         * 
         * Getter/Setter: 13 / 13
         * cascadingDeletes [Done]
         * cleanupTriggers  [Done]
         * strictIPs  [Done]
         * realTimestamps  [Done]
         * impliciGroupby  [Done]
         * implicitOrderby  [Done]
         * searchableIPs  [Done]
         * functionalIndexes  [Done]
         * getWikiID  [Done]
         * isOpen [Done]
         * getServerVersion [Done]
         * getSoftwareLink [Done]
         * getSearchEngine [Done]
         * 
         * Database driver wrapper: 23 / 23
         * lastError [Done]
         * lastErrno [Done]
         * doQuery [Done]
         * tableExists [Done]
         * fetchObject [Done]
         * fetchRow [Done]
         * freeResult [Done]
         * numRows [Done]
         * numFields [Done]
         * fieldName [Done]
         * insertId [Done]
         * dataSeek [Done]
         * affectedRows [Done]
         * selectDB [Done]
         * strencode [Done]
         * conditional [Done]
         * wasDeadlock [Done]
         * ping [Done]
         * getStatus [Done]
         * setTimeout [Done]
         * lock [Done]
         * unlock [Done]
         * insert [Done]
         * select [Done]
         * 
         * Slave/master: 2 / 2
         * setFakeSlaveLag [Done]
         * setFakeMaster [Done]
         * 
         * Reflection: 6 / 6
         * fieldExists [Done]
         * indexInfo [Done]
         * fieldInfo [Done]
         * fieldType [Done]
         * indexUnique [Done]
         * textFieldSize [Done]
         * 
         * Generation: 16 / 16
         * tableName [Done]
         * addQuotes [Done]
         * makeList [Done]
         * makeSelectOptions [Done]
         * estimateRowCount [Done]
         * nextSequenceValue [Done]
         * useIndexClause [Done]
         * replace [Done]
         * deleteJoin [Done]
         * lowPriorityOption [Done]
         * limitResult [Done]
         * limitResultForUpdate [Done]
         * timestamp [Done]
         * encodeBlob [Done]
         * decodeBlob [Done]
         * buildConcat [Done]
         */
        
        ######################################
        # Getters and Setters
        ######################################
        
        /**
         * Returns true if this database supports (and uses) cascading deletes
         */
        function cascadingDeletes() {
                return true;
        }

        /**
         * Returns true if this database supports (and uses) triggers (e.g. on the page table)
         */
        function cleanupTriggers() {
                return true;
        }

        /**
         * Returns true if this database is strict about what can be put into an IP field.
         * Specifically, it uses a NULL value instead of an empty string.
         */
        function strictIPs() {
                return true;
        }
        
        /**
         * Returns true if this database uses timestamps rather than integers
        */
        function realTimestamps() {
                return true;
        }

        /**
         * Returns true if this database does an implicit sort when doing GROUP BY
         */
        function implicitGroupby() {
                return false;
        }

        /**
         * Returns true if this database does an implicit order by when the column has an index
         * For example: SELECT page_title FROM page LIMIT 1
         */
        function implicitOrderby() {
                return false;
        }

        /**
         * Returns true if this database can do a native search on IP columns
         * e.g. this works as expected: .. WHERE rc_ip = '127.42.12.102/32';
         */
        function searchableIPs() {
                return true;
        }

        /**
         * Returns true if this database can use functional indexes
         */
        function functionalIndexes() {
                return true;
        }
        
        /**
         * Returns a unique string representing the wiki on the server
         */
        function getWikiID() {
                if( $this->mSchema ) {
                        return "{$this->mDBname}-{$this->mSchema}";
                } else {
                        return $this->mDBname;
                }
        }
        
        
        ######################################
        # Setup
        ######################################
        
        
        /**
         * 
         * @param string $server hostname of database server
         * @param string $user username
         * @param string $password
         * @param string $dbName database name on the server
         * @param function $failFunction (optional)
         * @param integer $flags database behaviour flags (optional, unused)
         */
        public function DatabaseIbm_db2($server = false, $user = false, $password = false,
                                                        $dbName = false, $failFunction = false, $flags = 0,
                                                        $schema = self::USE_GLOBAL )
        {

                global $wgOut, $wgDBmwschema;
                # Can't get a reference if it hasn't been set yet
                if ( !isset( $wgOut ) ) {
                        $wgOut = NULL;
                }
                $this->mOut =& $wgOut;
                $this->mFailFunction = $failFunction;
                $this->mFlags = DBO_TRX | $flags;
                
                if ( $schema == self::USE_GLOBAL ) {
                        $this->mSchema = $wgDBmwschema;
                }
                else {
                        $this->mSchema = $schema;
                }
                
                $this->open( $server, $user, $password, $dbName);
        }
        
        /**
         * Opens a database connection and returns it
         * Closes any existing connection
         * @return a fresh connection
         * @param string $server hostname
         * @param string $user
         * @param string $password
         * @param string $dbName database name
         */
        public function open( $server, $user, $password, $dbName )
        {
                // Load the port number
                global $wgDBport_db2, $wgDBcataloged;
                wfProfileIn( __METHOD__ );
                
                // Load IBM DB2 driver if missing
                if (!@extension_loaded('ibm_db2')) {
                        @dl('ibm_db2.so');
                }
                // Test for IBM DB2 support, to avoid suppressed fatal error
                if ( !function_exists( 'db2_connect' ) ) {
                        $error = "DB2 functions missing, have you enabled the ibm_db2 extension for PHP?\n";
                        wfDebug($error);
                        $this->reportConnectionError($error);
                }

                if (!strlen($user)) { // Copied from Postgres
                        return null;
                }
                
                // Close existing connection
                $this->close();
                // Cache conn info
                $this->mServer = $server;
                $this->mPort = $port = $wgDBport_db2;
                $this->mUser = $user;
                $this->mPassword = $password;
                $this->mDBname = $dbName;
                $this->mCataloged = $cataloged = $wgDBcataloged;
                
                if ( $cataloged == self::CATALOGED ) {
                        $this->openCataloged($dbName, $user, $password);
                }
                elseif ( $cataloged == self::UNCATALOGED ) {
                        $this->openUncataloged($dbName, $user, $password, $server, $port);
                }
                // Don't do this
                // Not all MediaWiki code is transactional
                // Rather, turn it off in the begin function and turn on after a commit
                // db2_autocommit($this->mConn, DB2_AUTOCOMMIT_OFF);
                db2_autocommit($this->mConn, DB2_AUTOCOMMIT_ON);

                if ( $this->mConn == false ) {
                        wfDebug( "DB connection error\n" );
                        wfDebug( "Server: $server, Database: $dbName, User: $user, Password: " . substr( $password, 0, 3 ) . "...\n" );
                        wfDebug( $this->lastError()."\n" );
                        return null;
                }

                $this->mOpened = true;
                $this->applySchema();
                
                wfProfileOut( __METHOD__ );
                return $this->mConn;
        }
        
        /**
         * Opens a cataloged database connection, sets mConn
         */
        protected function openCataloged( $dbName, $user, $password )
        {
                @$this->mConn = db2_connect($dbName, $user, $password);
        }
        
        /**
         * Opens an uncataloged database connection, sets mConn
         */
        protected function openUncataloged( $dbName, $user, $password, $server, $port )
        {
                $str = "DRIVER={IBM DB2 ODBC DRIVER};";
                $str .= "DATABASE=$dbName;";
                $str .= "HOSTNAME=$server;";
                if ($port) $str .= "PORT=$port;";
                $str .= "PROTOCOL=TCPIP;";
                $str .= "UID=$user;";
                $str .= "PWD=$password;";
                
                @$this->mConn = db2_connect($str, $user, $password);
        }
        
        /**
         * Closes a database connection, if it is open
         * Returns success, true if already closed
         */
        public function close() {
                $this->mOpened = false;
                if ( $this->mConn ) {
                        if ($this->trxLevel() > 0) {
                                $this->commit();
                        }
                        return db2_close( $this->mConn );
                }
                else {
                        return true;
                }
        }
        
        /**
         * Returns a fresh instance of this class
         * @static
         * @return 
         * @param string $server hostname of database server
         * @param string $user username
         * @param string $password
         * @param string $dbName database name on the server
         * @param function $failFunction (optional)
         * @param integer $flags database behaviour flags (optional, unused)
         */
        static function newFromParams( $server, $user, $password, $dbName, $failFunction = false, $flags = 0)
        {
                return new DatabaseIbm_db2( $server, $user, $password, $dbName, $failFunction, $flags );
        }
        
        /**
         * Retrieves the most current database error
         * Forces a database rollback
         */
        public function lastError() {
                if ($this->lastError2()) {
                        $this->rollback();
                        return true;
                }
                return false;
        }
        
        private function lastError2() {
                $connerr = db2_conn_errormsg();
                if ($connerr) return $connerr;
                $stmterr = db2_stmt_errormsg();
                if ($stmterr) return $stmterr;
                if ($this->mConn) return "No open connection.";
                if ($this->mOpened) return "No open connection allegedly.";
                
                return false;
        }
        
        /**
         * Get the last error number
         * Return 0 if no error
         * @return integer
         */
        public function lastErrno() {
                $connerr = db2_conn_error();
                if ($connerr) return $connerr;
                $stmterr = db2_stmt_error();
                if ($stmterr) return $stmterr;
                return 0;
        }
        
        /**
         * Is a database connection open?
         * @return 
         */
        public function isOpen() { return $this->mOpened; }
        
        /**
         * The DBMS-dependent part of query()
         * @param  $sql String: SQL query.
         * @return object Result object to feed to fetchObject, fetchRow, ...; or false on failure
         * @access private
         */
        /*private*/
        public function doQuery( $sql ) {
                //print "<li><pre>$sql</pre></li>";
                // Switch into the correct namespace
                $this->applySchema();
                
                $ret = db2_exec( $this->mConn, $sql );
                if( !$ret ) {
                        print "<br><pre>";
                        print $sql;
                        print "</pre><br>";
                        $error = db2_stmt_errormsg();
                        throw new DBUnexpectedError($this,  'SQL error: ' . htmlspecialchars( $error ) );
                }
                $this->mLastResult = $ret;
                $this->mAffectedRows = NULL;    // Not calculated until asked for
                return $ret;
        }
        
        /**
         * @return string Version information from the database
         */
        public function getServerVersion() {
                $info = db2_server_info( $this->mConn );
                return $info->DBMS_VER;
        }
        
        /**
         * Queries whether a given table exists
         * @return boolean
         */
        public function tableExists( $table ) {
                $schema = $this->mSchema;
                $sql = <<< EOF
SELECT COUNT(*) FROM SYSIBM.SYSTABLES ST
WHERE ST.NAME = '$table' AND ST.CREATOR = '$schema'
EOF;
                $res = $this->query( $sql );
                if (!$res) return false;
                
                // If the table exists, there should be one of it
                @$row = $this->fetchRow($res);
                $count = $row[0];
                if ($count == '1' or $count == 1) {
                        return true;
                }
                
                return false;
        }
        
        /**
         * Fetch the next row from the given result object, in object form.
         * Fields can be retrieved with $row->fieldname, with fields acting like
         * member variables.
         *
         * @param $res SQL result object as returned from Database::query(), etc.
         * @return DB2 row object
         * @throws DBUnexpectedError Thrown if the database returns an error
         */
        public function fetchObject( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }
                @$row = db2_fetch_object( $res );
                if( $this->lastErrno() ) {
                        throw new DBUnexpectedError( $this, 'Error in fetchObject(): ' . htmlspecialchars( $this->lastError() ) );
                }
                // Make field names lowercase for compatibility with MySQL
                if ($row)
                {
                        $row2 = new BlankObject();
                        foreach ($row as $key => $value)
                        {
                                $keyu = strtolower($key);
                                $row2->$keyu = $value;
                        }
                        $row = $row2;
                }
                return $row;
        }

        /**
         * Fetch the next row from the given result object, in associative array
         * form.  Fields are retrieved with $row['fieldname'].
         *
         * @param $res SQL result object as returned from Database::query(), etc.
         * @return DB2 row object
         * @throws DBUnexpectedError Thrown if the database returns an error
         */
        public function fetchRow( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }
                @$row = db2_fetch_array( $res );
                if ( $this->lastErrno() ) {
                        throw new DBUnexpectedError( $this, 'Error in fetchRow(): ' . htmlspecialchars( $this->lastError() ) );
                }
                return $row;
        }
        
        /**
         * Override if introduced to base Database class
         */
        public function initial_setup() {
                // do nothing
        }
        
        /**
         * Create tables, stored procedures, and so on
         */
        public function setup_database() {
                // Timeout was being changed earlier due to mysterious crashes
                // Changing it now may cause more problems than not changing it
                //set_time_limit(240);
                try {
                        // TODO: switch to root login if available
                        
                        // Switch into the correct namespace
                        $this->applySchema();
                        $this->begin();
                        
                        $res = dbsource( "../maintenance/ibm_db2/tables.sql", $this);
                        $res = null;
        
                        // TODO: update mediawiki_version table
                        
                        // TODO: populate interwiki links
                        
                        $this->commit();
                }
                catch (MWException $mwe)
                {
                        print "<br><pre>$mwe</pre><br>";
                }
        }

        /**
         * Escapes strings
         * Doesn't escape numbers
         * @param string s string to escape
         * @return escaped string
         */
        public function addQuotes( $s ) {
                //wfDebug("DB2::addQuotes($s)\n");
                if ( is_null( $s ) ) {
                        return "NULL";
                } else if ($s instanceof Blob) {
                        return "'".$s->fetch($s)."'";
                }
                $s = $this->strencode($s);
                if ( is_numeric($s) ) {
                        return $s;
                }
                else {
                        return "'$s'";
                }
        }
        
        /**
         * Escapes strings
         * Only escapes numbers going into non-numeric fields
         * @param string s string to escape
         * @return escaped string
         */
        public function addQuotesSmart( $table, $field, $s ) {
                if ( is_null( $s ) ) {
                        return "NULL";
                } else if ($s instanceof Blob) {
                        return "'".$s->fetch($s)."'";
                }
                $s = $this->strencode($s);
                if ( is_numeric($s) ) {
                        // Check with the database if the column is actually numeric
                        // This allows for numbers in titles, etc
                        $res = $this->doQuery("SELECT $field FROM $table FETCH FIRST 1 ROWS ONLY");
                        $type = db2_field_type($res, strtoupper($field));
                        if ( $this->is_numeric_type( $type ) ) {
                                //wfDebug("DB2: Numeric value going in a numeric column: $s in $type $field in $table\n");
                                return $s;
                        }
                        else {
                                wfDebug("DB2: Numeric in non-numeric: '$s' in $type $field in $table\n");
                                return "'$s'";
                        }
                }
                else {
                        return "'$s'";
                }
        }
        
        /**
         * Verifies that a DB2 column/field type is numeric
         * @return bool true if numeric
         * @param string $type DB2 column type
         */
        public function is_numeric_type( $type ) {
                switch (strtoupper($type)) {
                case 'SMALLINT':
                case 'INTEGER':
                case 'INT':
                case 'BIGINT':
                case 'DECIMAL':
                case 'REAL':
                case 'DOUBLE':
                case 'DECFLOAT':
                        return true;
                }
                return false;
        }
        
        /**
         * Alias for addQuotes()
         * @param string s string to escape
         * @return escaped string
         */
        public function strencode( $s ) {
                // Bloody useless function
                //  Prepends backslashes to \x00, \n, \r, \, ', " and \x1a. 
                //  But also necessary
                $s = db2_escape_string($s);
                // Wide characters are evil -- some of them look like '
                $s = utf8_encode($s);
                // Fix its stupidity
                $from = array("\\\\",   "\\'",  '\\n',  '\\t',  '\\"',  '\\r');
                $to =   array("\\",             "''",   "\n",   "\t",   '"',    "\r");
                $s = str_replace($from, $to, $s); // DB2 expects '', not \' escaping
                return $s;
        }
        
        /**
         * Switch into the database schema
         */
        protected function applySchema() {
                if ( !($this->mSchemaSet) ) {
                        $this->mSchemaSet = true;
                        $this->begin();
                        $this->doQuery("SET SCHEMA = $this->mSchema");
                        $this->commit();
                }       
        }
        
        /**
         * Start a transaction (mandatory)
         */
        public function begin() {
                // turn off auto-commit
                db2_autocommit($this->mConn, DB2_AUTOCOMMIT_OFF);
                $this->mTrxLevel = 1;
        }
        
        /**
         * End a transaction
         * Must have a preceding begin()
         */
        public function commit() {
                db2_commit($this->mConn);
                // turn auto-commit back on
                db2_autocommit($this->mConn, DB2_AUTOCOMMIT_ON);
                $this->mTrxLevel = 0;
        }
        
        /**
         * Cancel a transaction
         */
        public function rollback() {
                db2_rollback($this->mConn);
                // turn auto-commit back on
                // not sure if this is appropriate
                db2_autocommit($this->mConn, DB2_AUTOCOMMIT_ON);
                $this->mTrxLevel = 0;
        }
        
        /**
         * Makes an encoded list of strings from an array
         * $mode:
         *        LIST_COMMA         - comma separated, no field names
         *        LIST_AND           - ANDed WHERE clause (without the WHERE)
         *        LIST_OR            - ORed WHERE clause (without the WHERE)
         *        LIST_SET           - comma separated with field names, like a SET clause
         *        LIST_NAMES         - comma separated field names
         */
        public function makeList( $a, $mode = LIST_COMMA ) {
                wfDebug("DB2::makeList()\n");
                if ( !is_array( $a ) ) {
                        throw new DBUnexpectedError( $this, 'Database::makeList called with incorrect parameters' );
                }

                $first = true;
                $list = '';
                foreach ( $a as $field => $value ) {
                        if ( !$first ) {
                                if ( $mode == LIST_AND ) {
                                        $list .= ' AND ';
                                } elseif($mode == LIST_OR) {
                                        $list .= ' OR ';
                                } else {
                                        $list .= ',';
                                }
                        } else {
                                $first = false;
                        }
                        if ( ($mode == LIST_AND || $mode == LIST_OR) && is_numeric( $field ) ) {
                                $list .= "($value)";
                        } elseif ( ($mode == LIST_SET) && is_numeric( $field ) ) {
                                $list .= "$value";
                        } elseif ( ($mode == LIST_AND || $mode == LIST_OR) && is_array($value) ) {
                                if( count( $value ) == 0 ) {
                                        throw new MWException( __METHOD__.': empty input' );
                                } elseif( count( $value ) == 1 ) {
                                        // Special-case single values, as IN isn't terribly efficient
                                        // Don't necessarily assume the single key is 0; we don't
                                        // enforce linear numeric ordering on other arrays here.
                                        $value = array_values( $value );
                                        $list .= $field." = ".$this->addQuotes( $value[0] );
                                } else {
                                        $list .= $field." IN (".$this->makeList($value).") ";
                                }
                        } elseif( is_null($value) ) {
                                if ( $mode == LIST_AND || $mode == LIST_OR ) {
                                        $list .= "$field IS ";
                                } elseif ( $mode == LIST_SET ) {
                                        $list .= "$field = ";
                                }
                                $list .= 'NULL';
                        } else {
                                if ( $mode == LIST_AND || $mode == LIST_OR || $mode == LIST_SET ) {
                                        $list .= "$field = ";
                                }
                                if ( $mode == LIST_NAMES ) {
                                        $list .= $value;
                                }
                                // Leo: Can't insert quoted numbers into numeric columns
                                // (?) Might cause other problems. May have to check column type before insertion.
                                else if ( is_numeric($value) ) {
                                        $list .= $value;
                                }
                                else {
                                        $list .= $this->addQuotes( $value );
                                }
                        }
                }
                return $list;
        }
        
        /**
         * Makes an encoded list of strings from an array
         * Quotes numeric values being inserted into non-numeric fields
         * @return string
         * @param string $table name of the table
         * @param array $a list of values
         * @param $mode:
         *        LIST_COMMA         - comma separated, no field names
         *        LIST_AND           - ANDed WHERE clause (without the WHERE)
         *        LIST_OR            - ORed WHERE clause (without the WHERE)
         *        LIST_SET           - comma separated with field names, like a SET clause
         *        LIST_NAMES         - comma separated field names
         */
        public function makeListSmart( $table, $a, $mode = LIST_COMMA ) {
                if ( !is_array( $a ) ) {
                        throw new DBUnexpectedError( $this, 'Database::makeList called with incorrect parameters' );
                }

                $first = true;
                $list = '';
                foreach ( $a as $field => $value ) {
                        if ( !$first ) {
                                if ( $mode == LIST_AND ) {
                                        $list .= ' AND ';
                                } elseif($mode == LIST_OR) {
                                        $list .= ' OR ';
                                } else {
                                        $list .= ',';
                                }
                        } else {
                                $first = false;
                        }
                        if ( ($mode == LIST_AND || $mode == LIST_OR) && is_numeric( $field ) ) {
                                $list .= "($value)";
                        } elseif ( ($mode == LIST_SET) && is_numeric( $field ) ) {
                                $list .= "$value";
                        } elseif ( ($mode == LIST_AND || $mode == LIST_OR) && is_array($value) ) {
                                if( count( $value ) == 0 ) {
                                        throw new MWException( __METHOD__.': empty input' );
                                } elseif( count( $value ) == 1 ) {
                                        // Special-case single values, as IN isn't terribly efficient
                                        // Don't necessarily assume the single key is 0; we don't
                                        // enforce linear numeric ordering on other arrays here.
                                        $value = array_values( $value );
                                        $list .= $field." = ".$this->addQuotes( $value[0] );
                                } else {
                                        $list .= $field." IN (".$this->makeList($value).") ";
                                }
                        } elseif( is_null($value) ) {
                                if ( $mode == LIST_AND || $mode == LIST_OR ) {
                                        $list .= "$field IS ";
                                } elseif ( $mode == LIST_SET ) {
                                        $list .= "$field = ";
                                }
                                $list .= 'NULL';
                        } else {
                                if ( $mode == LIST_AND || $mode == LIST_OR || $mode == LIST_SET ) {
                                        $list .= "$field = ";
                                }
                                if ( $mode == LIST_NAMES ) {
                                        $list .= $value;
                                }
                                else {
                                        $list .= $this->addQuotesSmart( $table, $field, $value );
                                }
                        }
                }
                return $list;
        }
        
        /**
         * Construct a LIMIT query with optional offset
         * This is used for query pages
         * $sql string SQL query we will append the limit too
         * $limit integer the SQL limit
         * $offset integer the SQL offset (default false)
         */
        public function limitResult($sql, $limit, $offset=false) {
                if( !is_numeric($limit) ) {
                        throw new DBUnexpectedError( $this, "Invalid non-numeric limit passed to limitResult()\n" );
                }
                if( $offset ) {
                        wfDebug("Offset parameter not supported in limitResult()\n");
                }
                // TODO implement proper offset handling
                // idea: get all the rows between 0 and offset, advance cursor to offset
                return "$sql FETCH FIRST $limit ROWS ONLY ";
        }
        
        /**
         * Handle reserved keyword replacement in table names
         * @return 
         * @param $name Object
         */
        public function tableName( $name ) {
                # Replace reserved words with better ones
                switch( $name ) {
                        case 'user':
                                return 'mwuser';
                        case 'text':
                                return 'pagecontent';
                        default:
                                return $name;
                }
        }
        
        /**
         * Generates a timestamp in an insertable format
         * @return string timestamp value
         * @param timestamp $ts
         */
        public function timestamp( $ts=0 ) {
                // TS_MW cannot be easily distinguished from an integer
                return wfTimestamp(TS_DB2,$ts);
        }

        /**
         * Return the next in a sequence, save the value for retrieval via insertId()
         * @param string seqName Name of a defined sequence in the database
         * @return next value in that sequence
         */
        public function nextSequenceValue( $seqName ) {
                $safeseq = preg_replace( "/'/", "''", $seqName );
                $res = $this->query( "VALUES NEXTVAL FOR $safeseq" );
                $row = $this->fetchRow( $res );
                $this->mInsertId = $row[0];
                $this->freeResult( $res );
                return $this->mInsertId;
        }
        
        /**
         * This must be called after nextSequenceVal
         * @return Last sequence value used as a primary key
         */
        public function insertId() {
                return $this->mInsertId;
        }
        
        /**
         * INSERT wrapper, inserts an array into a table
         *
         * $args may be a single associative array, or an array of these with numeric keys,
         * for multi-row insert
         *
         * @param array $table   String: Name of the table to insert to.
         * @param array $args    Array: Items to insert into the table.
         * @param array $fname   String: Name of the function, for profiling
         * @param mixed $options String or Array. Valid options: IGNORE
         *
         * @return bool Success of insert operation. IGNORE always returns true.
         */
        public function insert( $table, $args, $fname = 'DatabaseIbm_db2::insert', $options = array() ) {
                wfDebug("DB2::insert($table)\n");
                if ( !count( $args ) ) {
                        return true;
                }

                $table = $this->tableName( $table );

                if ( !is_array( $options ) )
                        $options = array( $options );

                if ( isset( $args[0] ) && is_array( $args[0] ) ) {
                }
                else {
                        $args = array($args);
                }
                $keys = array_keys( $args[0] );

                // If IGNORE is set, we use savepoints to emulate mysql's behavior
                $ignore = in_array( 'IGNORE', $options ) ? 'mw' : '';
                
                // Cache autocommit value at the start
                $oldautocommit = db2_autocommit($this->mConn);

                // If we are not in a transaction, we need to be for savepoint trickery
                $didbegin = 0;
                if (! $this->mTrxLevel) {
                        $this->begin();
                        $didbegin = 1;
                }
                if ( $ignore ) {
                        $olde = error_reporting( 0 );
                        // For future use, we may want to track the number of actual inserts
                        // Right now, insert (all writes) simply return true/false
                        $numrowsinserted = 0;
                }

                $sql = "INSERT INTO $table (" . implode( ',', $keys ) . ') VALUES ';

                if ( !$ignore ) {
                        $first = true;
                        foreach ( $args as $row ) {
                                if ( $first ) {
                                        $first = false;
                                } else {
                                        $sql .= ',';
                                }
                                $sql .= '(' . $this->makeListSmart( $table, $row ) . ')';
                        }
                        $res = (bool)$this->query( $sql, $fname, $ignore );
                }
                else {
                        $res = true;
                        $origsql = $sql;
                        foreach ( $args as $row ) {
                                $tempsql = $origsql;
                                $tempsql .= '(' . $this->makeListSmart( $table, $row ) . ')';

                                if ( $ignore ) {
                                        db2_exec($this->mConn, "SAVEPOINT $ignore");
                                }

                                $tempres = (bool)$this->query( $tempsql, $fname, $ignore );

                                if ( $ignore ) {
                                        $bar = db2_stmt_error();
                                        if ($bar != false) {
                                                db2_exec( $this->mConn, "ROLLBACK TO SAVEPOINT $ignore" );
                                        }
                                        else {
                                                db2_exec( $this->mConn, "RELEASE SAVEPOINT $ignore" );
                                                $numrowsinserted++;
                                        }
                                }

                                // If any of them fail, we fail overall for this function call
                                // Note that this will be ignored if IGNORE is set
                                if (! $tempres)
                                        $res = false;
                        }
                }

                if ($didbegin) {
                        $this->commit();
                }
                // if autocommit used to be on, it's ok to commit everything
                else if ($oldautocommit)
                {
                        $this->commit();
                }
                
                if ( $ignore ) {
                        $olde = error_reporting( $olde );
                        // Set the affected row count for the whole operation
                        $this->mAffectedRows = $numrowsinserted;

                        // IGNORE always returns true
                        return true;
                }
                
                return $res;
        }
        
        /**
         * UPDATE wrapper, takes a condition array and a SET array
         *
         * @param string $table  The table to UPDATE
         * @param array  $values An array of values to SET
         * @param array  $conds  An array of conditions (WHERE). Use '*' to update all rows.
         * @param string $fname  The Class::Function calling this function
         *                       (for the log)
         * @param array  $options An array of UPDATE options, can be one or
         *                        more of IGNORE, LOW_PRIORITY
         * @return bool
         */
        function update( $table, $values, $conds, $fname = 'Database::update', $options = array() ) {
                $table = $this->tableName( $table );
                $opts = $this->makeUpdateOptions( $options );
                $sql = "UPDATE $opts $table SET " . $this->makeListSmart( $table, $values, LIST_SET );
                if ( $conds != '*' ) {
                        $sql .= " WHERE " . $this->makeListSmart( $table, $conds, LIST_AND );
                }
                return $this->query( $sql, $fname );
        }
        
        /**
         * DELETE query wrapper
         *
         * Use $conds == "*" to delete all rows
         */
        function delete( $table, $conds, $fname = 'Database::delete' ) {
                if ( !$conds ) {
                        throw new DBUnexpectedError( $this, 'Database::delete() called with no conditions' );
                }
                $table = $this->tableName( $table );
                $sql = "DELETE FROM $table";
                if ( $conds != '*' ) {
                        $sql .= ' WHERE ' . $this->makeListSmart( $table, $conds, LIST_AND );
                }
                return $this->query( $sql, $fname );
        }
        
        /**
         * Returns the number of rows affected by the last query or 0
         * @return int the number of rows affected by the last query
         */
        public function affectedRows() {
                if ( !is_null( $this->mAffectedRows ) ) {
                        // Forced result for simulated queries
                        return $this->mAffectedRows;
                }
                if( empty( $this->mLastResult ) )
                        return 0;
                return db2_num_rows( $this->mLastResult );
        }
        
        /**
         * USE INDEX clause
         * DB2 doesn't have them and returns ""
         * @param sting $index
         */
        public function useIndexClause( $index ) {
                return "";
        }
        
        /**
         * Simulates REPLACE with a DELETE followed by INSERT
         * @param $table Object
         * @param array $uniqueIndexes array consisting of indexes and arrays of indexes
         * @param array $rows Rows to insert
         * @param string $fname Name of the function for profiling
         * @return nothing
         */
        function replace( $table, $uniqueIndexes, $rows, $fname = 'DatabaseIbm_db2::replace' ) {
                $table = $this->tableName( $table );

                if (count($rows)==0) {
                        return;
                }

                # Single row case
                if ( !is_array( reset( $rows ) ) ) {
                        $rows = array( $rows );
                }

                foreach( $rows as $row ) {
                        # Delete rows which collide
                        if ( $uniqueIndexes ) {
                                $sql = "DELETE FROM $table WHERE ";
                                $first = true;
                                foreach ( $uniqueIndexes as $index ) {
                                        if ( $first ) {
                                                $first = false;
                                                $sql .= "(";
                                        } else {
                                                $sql .= ') OR (';
                                        }
                                        if ( is_array( $index ) ) {
                                                $first2 = true;
                                                foreach ( $index as $col ) {
                                                        if ( $first2 ) {
                                                                $first2 = false;
                                                        } else {
                                                                $sql .= ' AND ';
                                                        }
                                                        $sql .= $col.'=' . $this->addQuotes( $row[$col] );
                                                }
                                        } else {
                                                $sql .= $index.'=' . $this->addQuotes( $row[$index] );
                                        }
                                }
                                $sql .= ')';
                                $this->query( $sql, $fname );
                        }

                        # Now insert the row
                        $sql = "INSERT INTO $table (" . $this->makeList( array_keys( $row ), LIST_NAMES ) .') VALUES (' .
                                $this->makeList( $row, LIST_COMMA ) . ')';
                        $this->query( $sql, $fname );
                }
        }
        
        /**
         * Returns the number of rows in the result set
         * Has to be called right after the corresponding select query
         * @param Object $res result set
         * @return int number of rows
         */
        public function numRows( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }
                if ( $this->mNumRows ) {
                        return $this->mNumRows;
                }
                else {
                        return 0;
                }
        }
        
        /**
         * Moves the row pointer of the result set
         * @param Object $res result set
         * @param int $row row number
         * @return success or failure
         */
        public function dataSeek( $res, $row ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }
                return db2_fetch_row( $res, $row );
        }
        
        ###
        # Fix notices in Block.php 
        ###
        
        /**
         * Frees memory associated with a statement resource
         * @param Object $res Statement resource to free
         * @return bool success or failure
         */
        public function freeResult( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }
                if ( !@db2_free_result( $res ) ) {
                        throw new DBUnexpectedError($this,  "Unable to free DB2 result\n" );
                }
        }
        
        /**
         * Returns the number of columns in a resource
         * @param Object $res Statement resource
         * @return Number of fields/columns in resource
         */
        public function numFields( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }
                return db2_num_fields( $res );
        }
        
        /**
         * Returns the nth column name
         * @param Object $res Statement resource
         * @param int $n Index of field or column
         * @return string name of nth column
         */
        public function fieldName( $res, $n ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }
                return db2_field_name( $res, $n );
        }
        
        /**
         * SELECT wrapper
         *
         * @param mixed  $table   Array or string, table name(s) (prefix auto-added)
         * @param mixed  $vars    Array or string, field name(s) to be retrieved
         * @param mixed  $conds   Array or string, condition(s) for WHERE
         * @param string $fname   Calling function name (use __METHOD__) for logs/profiling
         * @param array  $options Associative array of options (e.g. array('GROUP BY' => 'page_title')),
         *                        see Database::makeSelectOptions code for list of supported stuff
         * @param array $join_conds Associative array of table join conditions (optional)
         *                        (e.g. array( 'page' => array('LEFT JOIN','page_latest=rev_id') )
         * @return mixed Database result resource (feed to Database::fetchObject or whatever), or false on failure
         */
        public function select( $table, $vars, $conds='', $fname = 'DatabaseIbm_db2::select', $options = array(), $join_conds = array() )
        {
                $res = parent::select( $table, $vars, $conds, $fname, $options, $join_conds );
                
                // We must adjust for offset
                if ( isset( $options['LIMIT'] ) ) {
                        if ( isset ($options['OFFSET'] ) ) {
                                $limit = $options['LIMIT'];
                                $offset = $options['OFFSET'];
                        }
                }
                
                
                // DB2 does not have a proper num_rows() function yet, so we must emulate it
                // DB2 9.5.3/9.5.4 and the corresponding ibm_db2 driver will introduce a working one
                // Yay!
                
                // we want the count
                $vars2 = array('count(*) as num_rows');
                // respecting just the limit option
                $options2 = array();
                if ( isset( $options['LIMIT'] ) ) $options2['LIMIT'] = $options['LIMIT'];
                // but don't try to emulate for GROUP BY
                if ( isset( $options['GROUP BY'] ) ) return $res;
                
                $res2 = parent::select( $table, $vars2, $conds, $fname, $options2, $join_conds );
                $obj = $this->fetchObject($res2);
                $this->mNumRows = $obj->num_rows;
                
                wfDebug("DatabaseIbm_db2::select: There are $this->mNumRows rows.\n");
                
                return $res;
        }
        
        /**
         * Handles ordering, grouping, and having options ('GROUP BY' => colname)
         * Has limited support for per-column options (colnum => 'DISTINCT')
         * 
         * @private
         *
         * @param array $options an associative array of options to be turned into
         *              an SQL query, valid keys are listed in the function.
         * @return array
         */
        function makeSelectOptions( $options ) {
                $preLimitTail = $postLimitTail = '';
                $startOpts = '';

                $noKeyOptions = array();
                foreach ( $options as $key => $option ) {
                        if ( is_numeric( $key ) ) {
                                $noKeyOptions[$option] = true;
                        }
                }

                if ( isset( $options['GROUP BY'] ) ) $preLimitTail .= " GROUP BY {$options['GROUP BY']}";
                if ( isset( $options['HAVING'] ) ) $preLimitTail .= " HAVING {$options['HAVING']}";
                if ( isset( $options['ORDER BY'] ) ) $preLimitTail .= " ORDER BY {$options['ORDER BY']}";
                
                if ( isset( $noKeyOptions['DISTINCT'] ) || isset( $noKeyOptions['DISTINCTROW'] ) ) $startOpts .= 'DISTINCT';
                
                return array( $startOpts, '', $preLimitTail, $postLimitTail );
        }
        
        /**
         * Returns link to IBM DB2 free download
         * @return string wikitext of a link to the server software's web site
         */
        public function getSoftwareLink() {
                return "[http://www.ibm.com/software/data/db2/express/?s_cmp=ECDDWW01&s_tact=MediaWiki IBM DB2]";
        }
        
        /**
         * Does nothing
         * @param object $db
         * @return bool true
         */
        public function selectDB( $db ) {
                return true;
        }
        
        /**
         * Returns an SQL expression for a simple conditional.
         * Uses CASE on DB2
         *
         * @param string $cond SQL expression which will result in a boolean value
         * @param string $trueVal SQL expression to return if true
         * @param string $falseVal SQL expression to return if false
         * @return string SQL fragment
         */
        public function conditional( $cond, $trueVal, $falseVal ) {
                return " (CASE WHEN $cond THEN $trueVal ELSE $falseVal END) ";
        }
        
        ###
        # Fix search crash
        ###
        /**
         * Get search engine class. All subclasses of this
         * need to implement this if they wish to use searching.
         * 
         * @return string
         */
        public function getSearchEngine() {
                return "SearchIBM_DB2";
        }
        
        ###
        # Tuesday the 14th of October, 2008
        ###
        /**
         * Did the last database access fail because of deadlock?
         * @return bool
         */
        public function wasDeadlock() {
                // get SQLSTATE
                $err = $this->lastErrno();
                switch($err) {
                        case '40001':   // sql0911n, Deadlock or timeout, rollback
                        case '57011':   // sql0904n, Resource unavailable, no rollback
                        case '57033':   // sql0913n, Deadlock or timeout, no rollback
                        wfDebug("In a deadlock because of SQLSTATE $err");
                        return true;
                }
                return false;
        }
        
        /**
         * Ping the server and try to reconnect if it there is no connection
         * The connection may be closed and reopened while this happens
         * @return bool whether the connection exists
         */
        public function ping() {
                // db2_ping() doesn't exist
                // Emulate
                $this->close();
                if ($this->mCataloged == NULL) {
                        return false;
                }
                else if ($this->mCataloged) {
                        $this->mConn = $this->openCataloged($this->mDBName, $this->mUser, $this->mPassword);
                }
                else if (!$this->mCataloged) {
                        $this->mConn = $this->openUncataloged($this->mDBName, $this->mUser, $this->mPassword, $this->mServer, $this->mPort);
                }
                return false;
        }
        ######################################
        # Unimplemented and not applicable
        ######################################
        /**
         * Not implemented
         * @return string ''
         * @deprecated
         */
        public function getStatus( $which ) { wfDebug('Not implemented for DB2: getStatus()'); return ''; }
        /**
         * Not implemented
         * @deprecated
         */
        public function setTimeout( $timeout ) { wfDebug('Not implemented for DB2: setTimeout()'); }
        /**
         * Not implemented
         * TODO
         * @return bool true
         */
        public function lock( $lockName, $method ) { wfDebug('Not implemented for DB2: lock()'); return true; }
        /**
         * Not implemented
         * TODO
         * @return bool true
         */
        public function unlock( $lockName, $method ) { wfDebug('Not implemented for DB2: unlock()'); return true; }
        /**
         * Not implemented
         * @deprecated
         */
        public function setFakeSlaveLag( $lag ) { wfDebug('Not implemented for DB2: setFakeSlaveLag()'); }
        /**
         * Not implemented
         * @deprecated
         */
        public function setFakeMaster( $enabled ) { wfDebug('Not implemented for DB2: setFakeMaster()'); }
        /**
         * Not implemented
         * @return string $sql
         * @deprecated
         */ 
        public function limitResultForUpdate($sql, $num) { return $sql; }
        /**
         * No such option
         * @return string ''
         * @deprecated
         */
        public function lowPriorityOption() { return ''; }
        
        ######################################
        # Reflection
        ######################################
        
        /**
         * Query whether a given column exists in the mediawiki schema
         * @param string $table name of the table
         * @param string $field name of the column
         * @param string $fname function name for logging and profiling
         */
        public function fieldExists( $table, $field, $fname = 'DatabaseIbm_db2::fieldExists' ) {
                $table = $this->tableName( $table );
                $schema = $this->mSchema;
                $etable = preg_replace("/'/", "''", $table);
                $eschema = preg_replace("/'/", "''", $schema);
                $ecol = preg_replace("/'/", "''", $field);
                $sql = <<<SQL
SELECT 1 as fieldexists
FROM sysibm.syscolumns sc
WHERE sc.name='$ecol' AND sc.tbname='$etable' AND sc.tbcreator='$eschema'
SQL;
                $res = $this->query( $sql, $fname );
                $count = $res ? $this->numRows($res) : 0;
                if ($res)
                        $this->freeResult( $res );
                return $count;
        }
        
        /**
         * Returns information about an index
         * If errors are explicitly ignored, returns NULL on failure
         * @param string $table table name
         * @param string $index index name
         * @param string
         * @return object query row in object form
         */
        public function indexInfo( $table, $index, $fname = 'DatabaseIbm_db2::indexExists' ) {
                $table = $this->tableName( $table );
                $sql = <<<SQL
SELECT name as indexname
FROM sysibm.sysindexes si
WHERE si.name='$index' AND si.tbname='$table' AND sc.tbcreator='$this->mSchema'
SQL;
                $res = $this->query( $sql, $fname );
                if ( !$res ) {
                        return NULL;
                }
                $row = $this->fetchObject( $res );
                if ($row != NULL) return $row;
                else return false;
        }
        
        /**
         * Returns an information object on a table column
         * @param string $table table name
         * @param string $field column name
         * @return IBM_DB2Field
         */
        public function fieldInfo( $table, $field ) {
                return IBM_DB2Field::fromText($this, $table, $field);
        }
        
        /**
         * db2_field_type() wrapper
         * @param Object $res Result of executed statement
         * @param mixed $index number or name of the column
         * @return string column type
         */
        public function fieldType( $res, $index ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }
                return db2_field_type( $res, $index );
        }
        
        /**
         * Verifies that an index was created as unique
         * @param string $table table name
         * @param string $index index name
         * @param string $fnam function name for profiling
         * @return bool
         */
        public function indexUnique ($table, $index, $fname = 'Database::indexUnique' ) {
                $table = $this->tableName( $table );
                $sql = <<<SQL
SELECT si.name as indexname
FROM sysibm.sysindexes si
WHERE si.name='$index' AND si.tbname='$table' AND sc.tbcreator='$this->mSchema'
AND si.uniquerule IN ('U', 'P')
SQL;
                $res = $this->query( $sql, $fname );
                if ( !$res ) {
                        return null;
                }
                if ($this->fetchObject( $res )) {
                        return true;
                }
                return false;

        }
        
        /**
         * Returns the size of a text field, or -1 for "unlimited"
         * @param string $table table name
         * @param string $field column name
         * @return int length or -1 for unlimited
         */
        public function textFieldSize( $table, $field ) {
                $table = $this->tableName( $table );
                $sql = <<<SQL
SELECT length as size
FROM sysibm.syscolumns sc
WHERE sc.name='$field' AND sc.tbname='$table' AND sc.tbcreator='$this->mSchema'
SQL;
                $res = $this->query($sql);
                $row = $this->fetchObject($res);
                $size = $row->size;
                $this->freeResult( $res );
                return $size;
        }
        
        /**
         * DELETE where the condition is a join
         * @param string $delTable deleting from this table
         * @param string $joinTable using data from this table
         * @param string $delVar variable in deleteable table
         * @param string $joinVar variable in data table
         * @param array $conds conditionals for join table
         * @param string $fname function name for profiling
         */
        public function deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds, $fname = "DatabaseIbm_db2::deleteJoin" ) {
                if ( !$conds ) {
                        throw new DBUnexpectedError($this,  'Database::deleteJoin() called with empty $conds' );
                }

                $delTable = $this->tableName( $delTable );
                $joinTable = $this->tableName( $joinTable );
                $sql = "DELETE FROM $delTable WHERE $delVar IN (SELECT $joinVar FROM $joinTable ";
                if ( $conds != '*' ) {
                        $sql .= 'WHERE ' . $this->makeList( $conds, LIST_AND );
                }
                $sql .= ')';

                $this->query( $sql, $fname );
        }
        
        /**
         * Estimate rows in dataset
         * Returns estimated count, based on COUNT(*) output
         * Takes same arguments as Database::select()
         * @param string $table table name
         * @param array $vars unused
         * @param array $conds filters on the table
         * @param string $fname function name for profiling
         * @param array $options options for select
         * @return int row count
         */
        public function estimateRowCount( $table, $vars='*', $conds='', $fname = 'Database::estimateRowCount', $options = array() ) {
                $rows = 0;
                $res = $this->select ($table, 'COUNT(*) as mwrowcount', $conds, $fname, $options );
                if ($res) {
                        $row = $this->fetchRow($res);
                        $rows = (isset($row['mwrowcount'])) ? $row['mwrowcount'] : 0;
                }
                $this->freeResult($res);
                return $rows;
        }
        
        /**
         * Description is left as an exercise for the reader
         * @param mixed $b data to be encoded
         * @return IBM_DB2Blob
         */
        public function encodeBlob($b) {
                return new IBM_DB2Blob($b);
        }
        
        /**
         * Description is left as an exercise for the reader
         * @param IBM_DB2Blob $b data to be decoded
         * @return mixed
         */
        public function decodeBlob($b) {
                return $b->getData();
        }
        
        /**
         * Convert into a list of string being concatenated
         * @param array $stringList strings that need to be joined together by the SQL engine
         * @return string joined by the concatenation operator
         */
        public function buildConcat( $stringList ) {
                // || is equivalent to CONCAT
                // Sample query: VALUES 'foo' CONCAT 'bar' CONCAT 'baz'
                return implode( ' || ', $stringList );
        }
        
        /**
         * Generates the SQL required to convert a DB2 timestamp into a Unix epoch
         * @param string $column name of timestamp column
         * @return string SQL code
         */
        public function extractUnixEpoch( $column ) {
                // TODO
                // see SpecialAncientpages
        }
}
?>